Multiwinding discharge balance coil



Sep 2s, 1.928. 1,685,161

R. K. HONAMAN MULTIWINDING D ISGHARGE BALANCE COIL Filed Feb. 27. 1926 2 Mar await IN VEN TOR ATTORNEY p operatin routine and Patented Sept. 25', 1928.

, ,685,165 TATES PAT NTYQFFICE.

mcmnn s m ms, OF- B ooMEIELn, NEW JERSEY, ASSIGNOR- '10 AM RICAN TELEPHONE AND TELEGRAPH CO PANY, A CORPORATION orv NEW YORK;

' .MULTIWINDING DISCHARGE BALANCE corn.

Applicationled February 27, 1926. Serial No. 91,214. I

This'invention relates to'voltage limiting devices, and particularlyto a type of. multiwinding transformer which is designed to limit the magnitude of the potential that may be applied to a selected section of a circuit.

In the operationof telephone circuits, such for example, as long circuits, which a're'exposed to inductive interference by neighboring power circuits, trouble known as acoustic shock experienced, particularly by the telephoneoperators when a high potential surge is set up in the exposed circuit, due, for example, to the accidental grounding of the power circuit. The abnormal potential induced in the telephone line c-ircuitpro'- duces an abnormal click in the telephone head receiver ofthe operator. The result of such acoustic shock interferes with the normal 5 therefore, is detrimental to the service.

It is theobject of this invention to provide means for limiting thepotential that may be impressed by an exposed line circuit upon a circuit to be protected, such, for example, as an operators telephone circuit, so that .the current in the operators receiver cannever exceed a predetermined value regardless of the potential applied across the line circuit, thereby preventing what 1s known as acoustic shock. I The invention may be more fully understood from the following description, togetherfwith the accompanying drawing, in the Figures land 2 ofywhich are illustrated arrangementsofthe prior-art and one form of embodiment of'the invention. 'Like reference characters ha ve been used to denote like pai'tsinboth'figures. 1 l i InFig. 1 is shown :atelephone line circuit 1 which is exposed to inductive interference from the adj aoent power circuit 2. The telephone line'circuit l isconnected to an operators telephone circuit 8, shown schemata cally. While the circuit 8 has been referred to as an operators circuit, it is understood that this is'for purposes o'fillustration only and that any other circuit which iti'sv d'e-' sired tov protect from acoustic shock might be substituted therefor. However, as the effect of acoustic shock is usually most severe in'an operators telephone set, the invention has been described in connection therewith.

' Bridged across the line 1 in Fig. 1 is a discharge balance coil. It consists of a transformer having two windings 3 and 4 on a common core 7. The impedances of these two windings are carefully balanced. They con-' tam the same number of turns and are arranged to oppose'ea'chfother or to set up opposite fluxes in the core 7 Winding 3 is com nected to one conductor of circuit 1 and to a protector gap comprising the electrode 5 and the grounded plate electrode 10. VVindcircuit 1 and to a protectorgap comprising the electrode 6and the grounded plate electrode '10. With such an arrangement, when the protector gaps are broken down, or operated by high voltage, the protector gap d scharge currents flow through the two windings 3 and 4 of the transformer. The ch ef'function of a dischargebalance coil of this type is. to overcome the effect of unbalanced discharge characteristics between the two protector gaps. If we assumethat potentials of equal magnitude were applied to both sides of line 1 and that the discharges across the two protector gaps were unequal, wewould then have a, condition of unbalance which'would cause acoustic shock in the operators circuit 8. Howeverythe windings 3 ing 4' is connected to the other conductorof and 4, which liaveequal turns and are so poled as to oppose each other, will'tend to equalize the currentsthrough the two protector gaps and henceneutralize the effect'of an unequal discharge. In other words, by providing two coils ofthe type referred to, the current "through the operators circuit which produces the acoustic shock and is caused by unbalanced dischargecharacter- ,istics across the two protector gaps will be minimized. v h The operation'of a discharge balance coil of thistype has been shown-to assist markedly in reducing the intensity of acoustic shocks when the voltages appliedto the two "sides of the circuit are equalor of only a sma-ll diiference in their order of magnitude.

However,.when there is a large difierence'between thevoltages applied to each side of the line, including the, case where the protector gap on one side of the line doesnot break due to the drop of the discharge current through this high magnetizing impedance. In such a case the acoustic shock experienced may be more severe than that which would result it the coils 3 and 4 were not included in circuit. In other words, the discharge bah ance coil presents certain advantages over a discharge gap alone when the applied voltages are equal or only of slight difference in that it compensates for unequal discharge characteristics. However, under conditions where the difference in the applied voltages is very great or where one of the protector gaps fails to break down, the discharge balance coil is a detriment and a discharge gap alone would be preferable.

In accordance with this invention, the discharge coil is constructed as shown in Fig. 2 of three windings on a common core instead of only two balanced windings as in the arrangements of the prior art shown in Fig. 1 and heretofore described. Accordingly, a third winding 8 is provided on the common core 7. This third winding 8" will have a larger number of turns than either of the windings 3, and 4: and its terminals will be connected to the discharge gap 9. WVhen the voltages applied to the two sides of the line are of the same order of magnitude, the discharge currents through the opposing windings 3 and 4: will be approximately equal. As these windings oppose each other, there will be practically no flux set up in the core 7 and hence practically no voltage induced in winding 8. Under these conditions the protective device will operate in substantially the same manner as the discharge coil of Fig. 1. If, however, the applied voltages are largely unbalanced so that the two currents are very ditierent, and particularly in the case where no discharge takes place on one side of the line resulting in zero current in the winding on that side, there will be a considerable voltage across the other winding which will result in a flux in the core 7 and hence an induced voltage in the third winding 8 to which the discharge gap 9 is connected. The ratio of turns to the third winding 8 would be so adjusted that the discharge gap 9 connected to it would break down at a predetermined voltage across one of the equal turn windings. hen this voltage is reached, the discharge gap 9 will break down and will close the circuit of the third winding 8. This has the effect of practically closing a short circuit around the winding carrying the discharge current. Accordingly, the impedance presented by this winding is removed or greatly reduced, thereby lowering the voltage from that side of the line in ground.

The limiting value of the voltage in one of the equal windings 3 and 4 which causes the breakdown of the gap 9 connected to the third winding 8 should be so chosen that the gap 9 will not break down on the small difl'crence in voltage required to balance the discharge when the applied voltages are only slightlydiflferent. For example, the two applied voltages may lie one above and the other below the breakdown voltage of the two protector discharge gaps. In this case it is de sirable to permit the discharge current in the winding connected to the side of the line to which the higher voltage is applied, to induce a voltage on the opposite side suflicient to bring the applied voltage on that side to a value that will break down the second protector. If the gap 9 were operated at a very low voltage, this action would be interfered with.

lVhile the invention has been disclosed in certain specific arrangements which are deemed desirable, it is understood that it is capable of embodiment in many other and widely varied forms without departing from the spirit of the invention as defined by the appended claims.

\Vhat is claimed is:

1. Aline circuit exposed to inductive interference, a circuit to be protected associated therewitlnand a protective device compris ing a multiwinding transformer having two equal turn windings differentially arranged on a common core, each of said windings connecting a protector gap to diiferent sides of said line circuit, and an auxiliary winding mounted on said common core and having a greater number of turns than either of said equal turn windings, and a spark gap across the terminals of said third winding.

2. A line circuit exposed to inductive interference, a circuit to be protected associated therewith, and a protective device comprising a multi-winding transformer having two equal turn windings differentially arranged on a common core, each of said windings connecting aprotector gap to opposite sides of said line circuit, and a third winding mounted on said common core having a spark gap across the terminals of said third winding adapted to operate at a definite potential in said winding.

In testimony whereof, I have signed my name to this specification this 25th dayof February, 192

RICHARD K. HONAMAN. 

